1. Field of the Invention
The present invention relates to a method and device for preventing engine knock during engine off-idle and, more particularly, to a method and device for preventing engine knock during engine off-idle in which the opening and closing of a throttle valve is controlled so as to effectively mix fuel and air.
2. Description of Related Art
Various types of knock-preventing devices for a vehicle engine are known in the art. These devices are generally controlled as part of an engine management system (EMS). The EMS generally includes an idle speed actuator (hereinafter "ISA") system. The ISA system is operated by an electronic control unit (hereinafter "ECU") to maintain a best target engine speed while the engine idles. For example, the ECU will increase the target engine speed when the load on the idling engine increases, such as during operation of the air conditioning system.
FIG. 1 is a diagrammatic top plane view of a conventional ISA unit 50. As shown in FIG. 1, such a conventional ISA unit 50 is located in an airflow path that is connected to a throttle body 62 at one end thereof and connected to a surge tank 58 at the other end thereof. The throttle body 62 defines another airflow path and is provided with a throttle valve assembly 52, including throttle valve 52a, and an axle cable 56 connected to throttle valve assembly 52 for opening and closing the throttle valve 52a.
In operation, during an idle driving state, the throttle valve 52a closes the airflow path in throttle body 62 and fresh air is supplied to the surge tank 58 through the ISA unit 50. The air in the surge tank 58 is then injected into a cylinder head 60. An ECU 64 controls the ISA system.
Such a conventional knock-preventing device including the ISA unit 50 suffers from a number of problems. For example, when a vehicle using the conventional ISA system climbs an uphill road and the driver suddenly depresses the accelerator pedal, the engine enters an off-idle state such as WOT (wide open throttle while idling). Consequently, the intake air flow is poor because the engine is at a lower (i.e., idling) rpm relative to the amount that of the throttle valve 52a is opened. Therefore, the air intake response is poor, and the fuel and air are not mixed properly. As a result, knocking occurs in the combustion chamber caused by partial explosion of air/fuel mixture (i.e., unstable combustion).